In the 3rd Generation Partnership Project (3GPP) (registered trademark), a radio access method and a radio network for cellular mobile communications (hereinafter referred to as “long term evolution (LTE)” or “evolved universal terrestrial radio access (EUTRA)”) have been considered.
LTE supports a frequency division duplex (FDD) and a time division duplex (TDD). LTE that employs an FDD scheme is also referred to as FD-LTE or LTE FDD. TDD is a technique that enables full duplex communication in at least two frequency bands by performing frequency division multiplexing on an uplink signal and a downlink signal. LTE that employs a TDD scheme is also referred to as TD-LTE or LTE TDD. TDD is a technique that enables full duplex communication in a single frequency band by performing time division multiplexing on an uplink signal and a downlink signal. Details of FD-LTE and TD-LTE are disclosed in NPL 1.
Furthermore, the base station device is able to transmit to the terminal device a reference signal (also referred to as RS) that is a known signal between the base station device and the terminal device. The reference signal is used for various purposes such as signal or channel demodulation, a channel state report, or the like, and it is possible to transmit a plurality of reference signals. For example, a cell-specific reference signal is transmitted in all downlink subframes as a reference signal specific to a cell. In addition, for example, a terminal-specific reference signal is transmitted in a resource in which a data signal that relates to the terminal device is mapped as a reference signal that is specific to the terminal device. Details of the reference signal are disclosed in NPL 1.
Small cell introduction is investigated in 3GPP. Small cell is a generic term for a cell having small coverage in which the transmit power of the base station device that constitutes the cell is small compared with a conventional cell (macro cell). For example, it is possible to locate small cells with high density and achieve an improvement of frequency efficiency per area by applying the small cells in a high frequency band. In the introduction investigation of the small cells, a technique in which the base station device is switched to a stopping state is investigated in order to achieve low power consumption, an inter-cell interference reduction, and the like. Details are disclosed in NPL 2.
In the 3GPP, since radio resources (communication resources) are scarce in a licensed band that is a frequency band that has been used up to now for mobile phones and the like, due to an increase of communication volume, providing LTE communication/LTE service on an unlicensed band that is an unlicensed frequency band (for example, 5 GHz) that is used for wireless LAN, Bluetooth (BT) (registered trademark), or the like has been investigated. Here, LTE communication/LTE service in an unlicensed band is referred to as LAA (licensed assisted access using LTE, LTE-advanced in unlicensed spectrum, licensed assisted access to unlicensed spectrum). A technical problem and a solution therefor are investigated in order for coexistence of a wireless LAN (WLAN: wireless local area network, Wi-Fi (registered trademark): wireless fidelity) and an LAA. Details are disclosed in NPL 3.